It has been proposed to mount an air bag system as a pedestrian protection device on a vehicle for protecting a human (e.g., a pedestrian) collided with the vehicle. Such an air bag system expands an air bag at a time when the vehicle collides with a pedestrian so as to protect the head and chest of the pedestrian from colliding with a windshield of the vehicle and A-pillars located at sides of the windshield. To expand the air bag, it is necessary to immediately determine whether an object collided with the vehicle is a human (e.g., pedestrian) or an obstacle that does not need the expansion of the air bag.
For example, Japanese Publication No. 2003-535769 (U.S. Pat. No. 6,784,792 B2) discloses an apparatus for recognizing an object collided with a vehicle. The apparatus has a first sensor mounted at a middle portion of a front side of a hood and a second sensor along to a bumper cover. The first sensor detects a load applied to the middle portion of the front end of the hood. The second sensor detects a load applied to the bumper cover. The apparatus determines whether or not an object collided with the vehicle is a pedestrian by comparing the loads detected by the first and second sensors.
However, since the first sensor is arranged at the middle portion of the front side of the hood, it may be difficult to accurately detect a collision load applied to a right end and a left end of the hood. To solve this problem, it can be considered to arrange the sensor thoroughly along the front end of the hood, i.e., from a front right end to a front left end of the hood. In this case, however, the size of the sensor increases.